A metrology technique for analyzing a substrate includes storing data indicating a boundary of an area in a 2-dimensional color space having a pair of color channels including a first color channel and a second color channel as axes of the color space, receiving color data of a substrate from a camera, generating a color image of the substrate from the color data, performing a comparison of a pair of color values for the pair of color channels for the pixel to the boundary of the area in the 2-dimensional color space for each pixel of a plurality of pixels of the color image to determine whether the pair of color values meet thresholds provided by the boundary, and generating a signal to an operator based on results of the comparison for the plurality of pixels.